Electrocoating systems for workpieces such as car bodies conventionally comprise an elongated tank and a system for conveying the workpieces in a continuous motion through the tank. The workpieces are angulated during entry into the tank, which helps expel trapped air. The workpieces are also angulated during exit from the opposing end of the tank, which helps drain solution from the workpieces back into the tank.
Although continuous motion coating systems of the described character are well adapted for large-volume production, the expense associated with systems of this character makes them unsuited for production in lower volumes. Electrocoating of car bodies and other workpieces in such low-volume production is conventionally accomplished by lowering the workpieces in sequence into a vertical dip tank. Although systems of this character are better suited for the economics of low-volume production, there is a problem in that air can become trapped on the undersurfaces of the workpiece, deleteriously affecting the coating process. It is a general object of the present invention to provide a system for dipping workpieces such as car bodies into a tank such as an electrocoating tank in which the workpieces can be rocked or tilted during entry into and exit from the tank and/or while disposed within the tank to help expel air from the undersurfaces of the workpieces, and to help promote circulation of tank liquid around the workpieces. Another and related object of the present invention is to provide a system of the described character in which the workpiece carrier is stabilized during entry into and exit from the tank, and during rocking motion within the tank, so that the carrier and workpiece do not hit the sides or ends of the tank. A further and more specific object of the present invention is to provide a system of the described character that is economical to implement, and that can be readily retrofitted into existing dip tank systems.
A system for dipping workpieces into a tank in accordance with a presently preferred embodiment of the invention comprises a conveyor disposed above the tank and a workpiece carrier movable on the conveyor along a path above the tank. Means on the conveyor selectively lower the carrier from the conveyor path into the tank, and provide for rocking the carrier within the tank. A track engages the carrier during lowering into the tank and stabilizes position of the carrier during rocking within the tank, and during entry into and exit from the tank, so that the carrier and workpieces carried thereby do not hit the sidewalls of the tank.
The carrier in the preferred embodiment of the invention takes the form of a box frame having pivotal connections at each corner for accommodating rocking of the frame while horizontal position of the frame is maintained by the track. Spaced guide rollers on the frame engage rails of the track as the frame is lowered into the tank. In order to accommodate motion of the carrier along the conveyor into alignment with the track, the track rails define a slot for passage of the guide rollers therethrough, and a pair of trap blocks for selectively closing the slot and capturing the guide rollers between the track rails. The trap blocks include longitudinally extending and vertically angulated cam fingers for camming the guide rollers into position between the track rails, and thereby accommodating slight longitudinal misalignment of the rollers with respect to the track rails. The track also includes a camming surface oriented at an angle to the longitudinal direction of motion for camming the rollers into the track slot, and thereby accommodating slight lateral misalignment of the carrier guide rollers with respect to the track slot.